This invention relates to a mechanism for clamping and holding an elongated workpiece for processing.
Polyvinyl tubing is commonly used for many purposes, such as fencing, lawn furniture, etc. Such applications require that the tubing be processed by, for example, forming openings in the side walls of the tubing to accommodate other components of the article being manufactured. This processing is commonly carried out by a template guided router which is used to cut openings in the sides of the tubing. Obviously, it is necessary to support, align, and center the tubing while it is being processed, but it is also necessary to be able to quickly insert and remove the tubing from the processing equipment. Although the particular embodiment disclosed herein relates to polyvinyl tubing and the processing of such tubing by cutting openings in the sides of the tubing, the clamping device disclosed may also be used in other types of processing, and with other elongated workpieces. The workpieces must be held securely in a predetermined location as the workpiece is being processed. It is also desirable that the clamp center the workpiece relative to the processing equipment and also quickly engage and release the workpiece. Furthermore, the clamping mechanism should be relatively simple and inexpensive. Prior art devices for clamping and holding elongated workpieces include relatively complicated rails, threaded shafts, and other components which are relatively difficult to align and maintain. These prior art devices involve many moving parts, and the clamping force exerted is limited and often insufficient.
According to the present invention, the workpiece is supported on a conveyor, which may be raised and lowered to accommodate tubing of different sizes. Gaps are provided in the conveyor through which arms extend that are pivotally connected with longitudinally extending clamping members which are guided for transverse movement relative to the workpiece by bearings slidable on a transversely extending rail. The arms are components of a camming mechanism and are connected to rotating plates which are rotatably mounted on the support and which is connected to the other rotating plates operating the clamping members by tie rods. One or more power cylinders are provided for rotating the plates. Accordingly, upon rotation of the plates, the clamping members are moved inwardly toward the center line of the conveyor to engage the workpiece and, when released, move away from the centerline thereby releasing the workpiece. Accordingly, since the clamping members move relative to the center line, the mechanism automatically centers the workpiece along the center line of the conveyor, and the clamping members can accommodate tubing of various sizes since the clamping members are moved inwardly toward the center line of the apparatus until they engage the workpiece.